Electrolytic cell and battery



July 21, 1953 ml TI Patented July 21, 1953 ELECTROLYTIC CELL AND BATTERY Robert A. A. Jeannin, Paris, France, assigner to Societe des Accumulateurs Fixes & de Traction, Romainville, France, a French body corporate Application-October23, 1951, Serial No. 252,645 In France December 9, 1950 (Cl. 13G-24) 16 Claims.

This invention relates to electrolytic cells or storage batteries capable vof being and remaining tightly enclosed orsealed at all times. It has been proposed heretofore to tightly enclose or seal lsuch cells or .batteries but such lenclosure or sealing has not been practicable because of the evolution and accumulation of `gas lwithin the battery casing.

Batteries of the `type employing alkaline electrolyte are greatly improved -by 'the embodiment of my invention therein.

The object Aof Athis invention is to provide a cell or 4battery having 'the usual positive and negative electrodes and v-an electrolyte, and a method -of producing the same, which may remain closed or sealed during passage of current therethrough from an external source, 4during charging and even overcharging of the .electrodes, land during discharging.

I have found that if an electrolytic cell or storage battery is provided with a non-,conductive separator between, and closely engaged by, each pair of opposed faces of the electrodeplates and the separator is very thin and at `least semipermeable, there will not be such .evolution and accumulation of gas as will make necessary the venting of the battery or cell casing. I have also found that 'the `achievement .of the object of my invention is enhanced, if the face of the separator opposed -to the face of the plate is substantially in the configuration of a compression matrix of the face V.of said plate. yI have also found that the achievement ofthe object of my invention is enhanced by having at least the surfaces of the velectrode plates, which Aare lpposed to -a separator, micro-porous in Vconstruction, for example, as the result of being .formed 4from iinely divided `consolidated particles. I

have also found that a ycell or battery accomplishing fthe-object of this .invention 'can be pro'- duced by `arranging the electrode plates in alternation withlvery thin :compressible and distortable non-conductive separators which are at least semi-permeable and are Substantially .inert to the electrolyte and then compressing under high pressure the resulting stack rof vplates and separators to fform a unitary or consolidated block, and then saturating the block with electrolyte and placing it in a casing which may be and remain tightly closed or-sealed.

Cells or batteries made in accordance with this invention release no visible gas when current is being passed through the cell or .battery or durwhether the container is sealed or open to the atmosphere; but in-'the interest of preservation .of the purity of the electrolyte and ease tof handling of the battery, it is Ypreferable that the battery be denitely closed at the completion of its construction. Sealing vis in no way necessary to the functioning of the battery.

Theories have been advanced concerning the absorption by the 4active material of one -plateof gases released at the other plate, but 'I am not certain as to the exact reasons why there is no visible release of gas in a battery made in vaccordance with this invention and, therefore, refrain tion for the absence of release-of gas. Y,

In the practice of my invention, the lpressure employed is las high as lig/cm;2 and the cornpression may result in a substantial reduction in thevolume of the assembly, for example, as much as 30%; and the compression may cause projectionson the surface of one eelctrode to project into depressions in the surface of the opposed electrode face. 'The latter effect may be enhanced by causing one electrode plate to be harder than the other vin order that projections on the hard plate m'ay form indentations in the softer plate.

vElectrode plates of any thickness may be employed but thinner plates are less brittle than thicker ones, more resistant to breakage during compression, and better suited to obtaining uniform impregnation with active material. Such thin plates afford more surface area in less volume. Such thin plates may have a thickness of the order of k1 millimeter orless.

Further objectsV and :advantages .and features of my linvention will appear from thefoillowing description of a specic construction, thev exampledescribed being an alkaline battery, which type of battery is .greatly ,improved Aby the embodiment -of my invention therein. In Vthis example of my invention, the micro-porous ,positive plate is made Yby sintering, for example at temperatures between 700 to 1000" C., of Very ne powder of suitablemetal, such as that obtainable by decomposition of nickel-carbonyl, and it is then impregnated with nickel 'hydrate in known manner. The negative plate may be similarly made from metal powder and impregnated in known manner vwith negative `active material vin which cadmium in a suitable form is the major active constituent. Or, the negative plate may be made by compressing, without substantial elevation of temperature, a mixture of finely divided copper particles of interlacing form such as dendritic, arborescent or needle-like crystals. mixed with powdered cadmium or cadmium hydrate or a powdered mixture of cadmium or cadmium hydrate with iron.

Such electrodes are mircro-porous and will absorb and retain a high percentage of electrolyte.

YIn the practice of this invention, the separators are made of materials which are substantially inert to or unattacked by the electrolyte; and in the example above-described the separator may consist of cellulosic material such as closely woven cotton fabric which has preferably previously been mercerized, or the separator may be any porous, semi-porous or micro-porous and compressible and distortable material which is substantially inalterable in use. The separator may be a sheet of cellophane.

The positive and negative plates are arranged in alternation and between all of the opposed faces a separator is positioned. The assembly is then highly compressed and the faces of the i separator are, by reason of the compressibility and distortability of the separator, formed into substantially the configuration of a compression-matrix of the opposed face of the electrode, leaving a minimum of unoccupied spaces between the opposed faces of the electrodes. After the compression which will substantially reduce the volume of the assembly, the plates and separator are in a more or less unitary form or a consolidated block. The positive plates are connected together and the negative plates are ccnnected together and the consolidated assembly is saturated with electrolyte. The saturation may be effected by mere soaking or by first creating a high vacuum within the assembly and then immersing it in the electrolyte and releasing the vacuum in order that atmospheric pressure will force the electrolyte into all the interstices of the assembly.

In order to afford a clear understanding of the relation of plates and separators, there is shown in the drawings the opposed electrode plates and the separator before and after compression.

In the drawings:

Figure 1 is a cross-sectional view, highly magnified, of micro-porous surface portions of pposed electrodes, with an uncompressed separator between the faces;

Figure 2 shows the same assembly after cornpression;

Figure 3 is a discharge diagram of the storage battery described in this example.

In Fig. 1, the highly magnified sectional proles of plates i and 2 are shown as having irregularities due to their formation from materials in the form of powder, and the separator 3 which is about .01 inch thick lies between the electrode faces. After application of pressure in the direction shown by the arrows F, the faces of the separator are formed into substantially the form of a compression-matrix of the opposed faces of the electrode plates leaving a minimum of unoccupied space between those faces. As a result of the compression, projections on one plate'are more or less tted into indentations on the opposed plate, and the projections are at least partly flattened out, with the result that vthe average distance between the faces of the plates is made more uniform. As above pointed out, this result may be enhanced by having one of the plates softer than the other.

The compressed assembly, above referred to, after saturation with electrolyte is enclosed in a casing .which preferably tightly surrounds the assembly and holds the plate-faces in close engagement with the separators and may even exert a continuing compression of the separators.

Preferably, additional electrolyte is added and the casing may or may not then be tightly enclosed or sealed. In the operation of such a battery, or even an electrolytic cell made as above described but omitting the active material from the plates, continuous passage of current through the battery or cell will not produce any visible release of gas, and the battery shows no visible release of gas during charging or overcharging or discharging. This absence of gas release occurs with the use of micro-porous plates and very thin separators lying in close contact between the opposed faces of the electrodes; but I do not attempt a theoretical explanation of the cause of this result.

The absence of gas release hasbeen demonstrated in the following examples:

Example 1 Twenty-four plates of sintered nickel powder having each a surface of 13 sq. cm. (about 2 sq. in.) and a thickness of .6 mm. (about .0236") were subjected to a uniform pressure of kg./sq. cm. (about 1,422 p. s. i.), separators of close-wovencotton fabric .15 mm. (about .006") thick being interposed between the plates. The aggregate nal thickness of the assembly amounted to 12 mm. (.473"). This assembly was then immersed in a jar containing a potash solution at 24 B., every other plate being interconnected and the two series thus obtained being further connected to the terminals of a D. C'.

source.

When the current flowing across the thus obtained electrolyte cell ranged from zero to 100 milliamperes, no gaseous release was visible. At 100 milliamperes the terminal voltage of the cell was stabilized at 1.35 volts, this being a practically definite level.

On the contrary, a similar cell made according to the practice now conventional in the art, i. e., without compression, at the same current intensity of 100 milliamperes, showed a voltage of 1.56 to 1.58 volts and a visible gaseous release occurred.

Example 2 Forty positive and forty negative plates, i. e., eighty plates, similar to those described in Example 1 but impregnated with positive and negative active material, respectively, with interposition therebetween of similar cotton separators, were subjected as above to a pressure of 100 leg/sq. cm. (1,422 p. s. i.) whereby the total thickness is reduced to 40 mm. (1.6"). The capacity of this assembly as determined from the weight of active material impregnated into the plates was then found to be 6 ampere-hours. The thus obtained block of pressed plates was then immersed in an open-top jar containing a potash solution at 24 B. rIhis battery was then charged at a charging rate of 1.5 amperes, i. e. denitely higher than the normal charging rate which, as known, is equal to one-fifth of the ampere-hours capacity, in amperes, which in the present instance means 1.2 amperes. After a 15-hour charge, corresponding to a charge of 22.5 amperehours and therefore to a considerable overcharge of the battery, the terminal voltage was only 1.46 volts. Moreover, it was observed that this final voltage at completion of charge was maintained without gaseous release during an overcharge lasting several days at a .fi-ampere rate. By way of comparison, a storage battery madeV of the same elements but without subjecting the latter to the pressure defined above, shows. a 1.60 to 1.75-volt potential range with a strong gaseous release after a maximum charging time of 8 hours at the same rating of 1.5 amperes.

A number of subsequent experiments made with the'compressed-cell battery showed that the terminal voltage was never above 1.48 volts. In each test an open jar was used.

Example 3 After having fully charged and even overcharged the battery described in Example 2, the same battery was discharged with a two-ampere load, corresponding to'one-third of the amperehour capacity of the battery. The average voltage at the terminals of the battery was about 1.25 volts. In relation to time, this voltage decreased rather slowly at first, as illustratedby the curve D, Fig. 3, and then dropped very sharply to zero, practically, when the battery was discharged. At this moment, the same current strength was kept circulating in the same direction acrossthe battery from an auxiliary source, whereby the battery was put in the condition of inverted charge. Terminal voltage measurements are plotted in curve I forming the extension of curve D, Fig. 3. As illustrated by this curve,the reversed voltage of the battery began to rise in absolute value and then dropped very quickly until it was stabilized at about 0.10 volt, without any visible gaseous release.

This phenomenon of extremely low voltage of the inverted charge is very important because it CFI makes it possible to connect in series battery cells made in accordance with this invention without the danger that inversion of one batterycell will cause any substantial decrease in the output voltage of the series. When battery cells are connected in. series, inversion of one of the cells is not unusual because the capacities of the batteries/are not all alike and the first battery discharged will become reversed. In 'batteries of conventional construction, the reversal shows a reversed voltage of 1.50 to 1.70 volts and a substantial release of gas occurs. In comparison, when using batteries `made according to this invention, the reverse voltage remains low and there is no substantial release of gas.

Since there is no release of gas in batteries made in accordance with thisinvention, thev charging current elciency, being the ratio of the amount of current chemically transformingactive.material to the total impressed current, is the same on both plates at all times. While there is theoretically no advantage in using electrodes having different capacities, the advantage of the low reversing current in the batteries of this invention can be retained by making one electrode, preferably the negative electrode, with a higher capacity than the other andgiving it an initial charge not substantially in excess of the difference in capacity, thus preventing the simultaneous reversal of both electrodes. This can be accomplished by incorporating in one electrode an electro-chemically greater amount of active material than is incorporated in the other. The electrode of higher capacity is then given a charge exceeding that of the electrode of lower capacity by an amount not in excess of such difference of capacity, before the electrodes are assembled inthe battery.

In 'batteries made according to this invention, the amount of electrolyte present in the cell may be limited substantially to that which is retained by capillarityl in the pores Vof the block or assembly constituted by the compressed plates and separators, but as a precaution, a little additional electrolyte may be present. When completed by compression, the block or assembly consists of plates of opposed polarity having their faces separated substantially only by separators and the distance between those faces may be of the order of one-tenth of a millimeter (.004) up to a few tenths of a millimeter (.02")'. References herein to thin separators are intended as a reference to a separator which after the compression step will cause the faces of the plates, which closely er1- gage the separator, to be spaced a distance within the range last mentioned. The separators are substantially in register with and at leastcoextensive with the opposed plate faces.

From the foregoing, it will be apparent that4 while some of the features of my invention have independentivalue, the best results are obtainable when the plates or electrodes are micro-porous, close contact between the opposed faces of'electrodes and the separator is established as by compression and maintained, and the separator is' thin.

From the foregoing, it will be apparent that the absence of release of gas makes possible the tight closing of the battery casing or jar. It has been observed that when the batteries of Examples 2 and 3 are tightly sealed, the charging voltage remains practically the same as the charging voltage Observed in the tests in an open-top jar.

The specific details contained in the foregoing description of examples of my invention are mentione'd for the purpose of facilitatingan understanding of my invention and not as limiting'it, and the references therein to alkaline electrolyte and to cadmium or cadmium and iron are not intended to'limit my invention thereto because my invention is applicable to electrode plates or blocks carrying any active materials and cooperating with any electrolytes known in the art. of batteries. My invention includes such variations and modifications as fall within the following claims.

What I claim is:

1. An electrolytic cell in which in normal operation the voltage at the terminals never exceeds 1.48 volts and which is, consequently, without substantial gas evolution, comprising an electrolyte, at least one positive electrode and one negative electrode located opposite one another, each electrode comprising consolidated finely-divided particles of a metal substantially unaffected by theelectrolyte, a thin, distortable diaphragm of non-conducting matter unaffected by the electrolyte and having a surface-at least equal to that of the adjacentfaces of the opposite electrodes, said diaphragm being closely engaged between the adjacent faces of the electrodes at least byv previously exerted strong pressure against the assembly of electrodes and diaphragm, whereby each face of the diaphragm is substantially in the configuration of a compression-matrix of the face ofthe adjacent electrode, and. said electrodes and said diaphragm being saturated with said electrolyte.

2. A secondary cell in which in normal operation the voltage at the terminals never exceeds 1.48 volts and which is, consequently, without substantial gas evolution, comprising anelectrolyte, at least one positive electrode and one negativey electrode located opposite one another, each electrode including consolidated finely-divided particles of metal substantially unaffected bythe electrolyte, the pores of which respectively ccn-V tain positive and negative active materials, a thin, distortable diaphragm of non-conducting matter substantially unaffected by the electrolyte and having a surface at least equal to that of adjacent faces of the opposite electrodes, said diaphragm being closely engaged between the adjacent faces of the electrodes at least by previously exerted pressure against the assembly of electrodes and diaphragm, whereby each face of the diaphragm is substantially in the form of a compression-matrix of the face of the adjacent electrode, and said electrodes and diaphragm being saturated with said electrolyte.

3. A secondary cell according to claim 2, wherein the diaphragm has, before compression, a thickness of at the most five-tenths of a millimeter.

4. A secondary cell according to claim 2, wherein the electrodes are in the form of plates, the thickness of which is at the most one millimeter.

5. A secondary cell according to claim 2, wherein at least each positive electrode is of sintered electrode type.

6. A secondary cell according to claim 2, wherein electrodes of at least one polarity are formed of metal particles of interlacing form consolidated by previous compression and each carries active materials in its pores. 7. A secondaryv cell according to claim 2, wherein the electrodes, diaphragm and electrolyte are enclosed in a gas and liquid-tight casing.

8. A secondary cell according to claim 2, wherein the electrolyte is alkaline and consists of alkali metal hydroxide solution.

9..A secondary cell according to claim 2, wherein the electrolyte is alkali metal hydroxide solution, wherein the positive active material includes nickel hydroxide and the negative active material includes cadmium in convenient chemical form as its main constituent.

10. A secondary cell according to claim 2, wherein the diaphragm is a non-conductive closely-woven fabric substantially unaffected by the electrolyte.

1l. A secondary cell according to claim 2, wherein a casing is included that is in close rnechanical contact relationship with the assembly of said electrodes and said diaphragms, whereby said electrodes and diaphragms are kept pressed against each other. Y

12. An electrolytic cell according to claim 1, wherein said electrodes each consist solely of sintered nickel powder and wherein said electrolyte is alkali metal hydroxide solution.

13. The method of constructing a secondary cell which comprises the steps of arranging alternately positive and negative electrodes composed of consolidated finely-divided particles of metal substantially unaffected by thel electrolyte and carrying suitable active materials in their pores, placing between faces of said electrodes, thin, compressible, distortable, non-conducting diaphragme substantially unaffected by the electrolyte, compressing together the assembled electrodes and diaphragms with a pressure of the order of at least 100 kg,/cm.2 so as to reduce the initial volume of the assembly up to 30% in the direction perpendicular to said faces, inserting the assembly in a casing which closely engages the compressed assembly and holds the electrodes and diaphragms in close engagement, saturating the compressed assembly with a suitable electrolyte and sealing the casing.

14. A cell operating without substantial gas evolution, comprising an electrolyte, at least one positive electrode and one negative electrode lo'- cated opposite one another, each electrode comprising consolidated finely-divided particles of a metal substantially unaffected by the electrolyte, a thin, distortable diaphragm of non-conducting matter substantially unaffected by the electrolyte and contacting and separating the adjacent faces of the opposite electrodes, said diaphragm being closely compressed between the adjacent faces of the electrodes, and each face of the diaphragm being substantially in the configuration of a compression-matrix of the face of the adjacent electrode, said electrodes and said diaphragms being permeated by said electrolyte.

15. A secondary cell operating without substantial gas evolution, comprising an electrolyte, at least one positive electrode and one negative electrode located opposite one another, each electrode including consolidated finely-divided particles of metal substantially unaffected by the electrolyte, the pores of which electrodes respectively contain positive and negative active materials, a thin, distortable diaphragm of nonconducting matter substantially unaffected by the electrolyte and contacting and separating the adjacent faces of the opposite electrodes, said diaphragm being closely compressed between the adjacent faces of the electrodes, and each face of the diaphragm being substantially in the configuration of a compression-matrix of the face of the adjacent electrode, and said electrodes and said diaphragm being permeated by said electrolyte.

16. The method of constructing a secondary cell which comprises the steps of arranging alternateiy positive and negative electrodes composed of consolidated finely-divided particles of metal substantially unaffected by the electrolyte and carrying suitable active materials in their pores, placing between faces of said electrodes, thin, compressible, distortable, non-conducting diaphragms substantially unaffected by the electrolyte, compressing together the assembled electrodes and diaphragms to form each face of the diaphragm into the configuration of a compression-matrix of the adjacent electrode, inserting the assembly in a casing which closely engages the compressed assembly and holds the electrodes in close engagement, permeating the compressed assembly with a suitable electrolyte and sealing the casing.

ROBERT A. A. JEANNIN;

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,377,194 Edison May 10, 1921 2,213,128 Langguth Aug. 27, 1940 2,554,125 Salauze May 22, 1951 2,561,943 Moulton et al. July 24, 1951 2,571,927 Neumann et al. Oct. 16, 1951 2,594,713 Andre Apr. 20, 1952 FOREIGN PATENTS Number Country Date 270,655 Switzerland Sept. 15, 1950 561,820 Great Britain June 6, 1944 

14. A CELL OPERATING WITHOUT SUBSTANTIAL GAS EVOLUTION, COMPRISING AN ELECTROLYTE, AT LEAST ONE POSITIVE ELECTRODE AND ONE NEGATIVE ELECTRODE LOCATED OPPOSITE ONE ANOTHER, EACH ELECTRODE COMPRISING CONSOLIDATED FINELY-DIVIDED PARTICLES OF A METAL SUBSTANTIALLY UNAFFECTED BY THE ELECTROLYTE, A THIN, DISTORTABLE DIAPHRAGM OF NON-CONDUCTING MATTER SUBSTANTIALLY UNAFFECTED BY THE ELECTROLYTE AND CONTACTING AND SEPARATING THE ADJACENT FACES OF THE OPPOSITE ELECTRODES, SAID DIAPHRAGM BEING CLOSELY COMPRESSED BETWEEN THE ADJACENT FACES OF THE ELECTRODES, AND EACH FACE OF THE DIAPHRAGM BEING SUBSTANTIALLY IN THE CONFIGURATION OF A COMPRESSION-MATRIX OF THE FACE OF THE ADJACENT ELECTRODE, SAID ELECTRODES AND SAID DIAPHRAGMS BEING PERMEATED BY SAID ELECTROLYTE. 